1. Field of the Invention
The invention relates generally to the field of polymer nanocomposites in oilfield applications, and more particularly to the use of functionalized graphene sheets (FGS), also known as thermal exfoliated graphite oxide (TEGO), for use in oilfield applications.
2. Background Art
Oil wells are typically drilled into the underground or subsea formations with depths of a couple miles or more. The environment in these deep wells are very harsh, with temperatures reaching 250° C. or higher and pressures of 20,000 psi or higher. In addition, the downhole environment contains various small molecule gases and liquids. The abilities of these small molecules to penetrate or permeate through polymers or seals are greatly enhanced under the high temperature and high pressure conditions. These conditions post great challenges to various tools and equipment that are used in drilling and exploring these wells, or are placed in the well during production. Many of these tools, pipes, valves, etc. include housings, sleeves, or seals to protect the inside components or to prevent fluid leakages. These devices would need to survive the harsh environment for the duration of their expected service lives. Therefore, materials that can survive the high temperature and high pressure environment are needed for the construction of these oilfield elements. Particularly, materials that can provide effective barriers to fluid permeation or penetration under high temperatures and high pressures are needed.
In recent years, the use of composite materials is gaining popularity. The composite materials typically comprise additives mixed in matrix materials. The additives are selected for their ability to endow or enhance the desired properties of the composites (such as barrier to fluid permeation). Commonly used composites in the oilfield applications, for example, include polymer-based nanocomposites, polymer-organoclays and polymer-carbon nanotubes (CNT) composites.
The use of graphite-containing or graphene-containing composites have also been proposed. Graphene sheets are individual layers of graphite. Each graphene sheet is composed of a honeycomb arrangement of carbon atoms via sp2 bonds. Graphene sheets are expected to have tensile modulus and ultimate strength values similar to that of single wall carbon nanotubes (SWCNT). Graphite is composed of multiple graphene sheets stacked and held together by van der Waal forces. Graphite is significantly cheaper than CNTs. This makes it an attractive material for downhole applications.
In addition, graphite can be modified to change its properties or to further enhance the desired properties. Common approaches to changing the properties of graphite include intercalation and oxidation reactions. For example, Schniepp et al., “Functionalized Single-Sheet Graphene by Oxidation and Thermal Expansion of Graphite: Exfoliation Mechanism and Characterization,” J. Phys. Chem., B 110, 8535-8539 (2006), discloses the formation of individual chemically modified graphene sheets by oxidation and thermal expansion of graphite. The expansion results from explosive exothermic decomposition of the oxygen-containing functional groups of graphite oxide into CO2 and water. See also, MaAllister et al., “Functionalized Single-Sheet Graphene by Oxidation and Thermal Expansion of Graphite: Exfoliation Mechanism and Characterization”, 2007 AIChE meeting abstract.
Similarly, Ozbas et al., “Multifunctional Elastomer Nanocomposites With Functionalized Graphene Single Sheets”, 2007 AIChE meeting abstract discloses functionalized graphene sheets. The functionalized graphene sheets (FGS) are obtained through rapid thermal expansion of graphite oxide. These functionalized graphene sheets have high aspects ratios (100-10000) and specific surface areas (1800 m2/g).
U.S. Patent Application publication No. 2007/0092432, which is incorporated by reference herein in its entirety, also discloses graphite oxides and thermally exfoliated graphite oxides. Graphite oxides are prepared by intercalation and oxidation of natural graphite. The graphite oxides thus formed can be exfoliated by rapid heating to produce the thermally exfoliated graphite oxide (TEGO) in a manner similar to that disclosed by McAllister et al.
The use of graphite or graphene-containing composites in the manufacture of downhole tools or elements have been disclosed in the co-pending U.S. patent application Ser. No. 11/306,119, published as U.S. Application publication No. 2007/0142547. Specifically, this application discloses the use of composites containing graphite nanoflakes or nanoplatelets.
While downhole tools made of graphite or graphene composites have proven useful, there remains a need for better materials and tools for downhole applications.